用FindWindow函数读取窗体句柄来指定消息框MessageBox属于具体的画面!
如:
指定为画面1:
HWND handle=NULL;
int iRet;
handle=FindWindow(NULL,"画面1");
iRet=MessageBox(handle,"画面1","对话框",MB_OKMB_ICONQUESTIONMB_SYSTEMMODAL);

指定为画面2:
HWND handle2=NULL;
int iRet2;
handle2=FindWindow(NULL,"画面2");
iRet2=MessageBox(handle2,"画面2","对话框",MB_OKMB_ICONQUESTIONMB_SYSTEMMODAL);